As one of migration managing methods in an Internet system, there is a Mobile IP, and Mobile IPv4 based on IPv4 is standardized in RFC 3220 (IP Mobility Support). The standardization of Mobile IPv6 based on IPv6 is currently proceeding as described in an Internet draft “draft-ietf-mobileip-ipv6 (Mobility Support in IPv6)”. By means of these protocols, a mobile terminal can perform communications using the same address when the mobile terminal moves between different networks.
In Mobile Ipv6, when a mobile terminal moves away from a home link, the terminal acquires prefix information of the currently connected link from network information transmitted by an access router device of the currently connected link. The mobile terminal generates a care-of address which is temporarily used in the link, from the prefix information of the link. After that, the mobile terminal registers the care-of address in a home agent on the home link of the mobile terminal as a primary care-of address by transmitting a binding update message to a home agent. The home agent receives the binding update message from the mobile terminal, then, makes or updates a binding cache entry which relates a home address with the care-of address.
After that, the home agent refers to the binding cache and receives, on behalf of the mobile terminal, a packet transmitted to the home address of the mobile terminal at the home link. Then, the home agent executes a processing of encapsulating the packet received on behalf of the terminal and forwarding it to the care-of address of the mobile terminal. The mobile terminal decapsulates the tunneled packet forwarded by the home agent, and thus can receive the packet addressed to the home address of the mobile terminal.
Providing the home agent function of mobility management to the mobile terminal in the home gateway device controlling relay processing between the home network and the Internet network as above has been considered to be preferable in view of forwarding efficiency compared with arrangement of the home agent in the home network, because the redirection can be achieved without forwarding the packet destined to the mobile terminal to the home network while the mobile terminal is accommodated in an foreign network.
One of methods of providing the home gateway device with IP addresses and information for setting the home network is using DHCP (Dynamic Host Configuration Protocol). DHCPv4 based on IPv4 is standardized in RFC 2131 (Dynamic Host Configuration Protocol), and is mainly used for providing terminals with IP addresses and information of servers allocated in the network. DHCPv6 based on IPv6 is disclosed in JP-A-2001-24710 and the standardization thereof is currently proceeding. By using the DHCPv6, network prefix information can be provided in addition to the functions provided by the DHCPv4. By having a DHCP server provide the home gateway device with prefix information for setting the home network, the home gateway device can construct the home network automatically. A method of distributing the network prefix information using the DHCPv6 is disclosed in an Internet draft “draft-ietf-dhc-dhcpv6-opt-prefix-delegation (IPv6 Prefix Options for DHCPv6)”, and the standardization work is currently proceeding.
In addition to the Internet draft and the like, home conventional gateway devices include the one disclosed in JP-A-2001-24710.
FIG. 14 is a configuration view of a mobile communication system disclosed in JP-A-2001-24710.
In FIG. 14, when a local network 1200 is connected to a wide area network 1500, a representative server 1010 of the local network 1200 tries to make a connection to a segment 1120. At that time, the representative server 1010 requests that an upper server 1020 which manages the segment 1120 allocate an address block. The representative server distributes the address block allocated as a result of this request in the local network 1200. Accordingly, the representative server 1010 can make an automatic management of the addresses efficiently at appropriate timing.
However, in the Internet drafts “draft-ietf-dhc-dhcpv6 (Dynamic Host Configuration Protocol for IPv6) and “draft-ietf-dhc-dhcpv6-opt-prefix-delegation (IPv6 Prefix Options for DHCPv6)”, the setting method of a home link, namely, a sequence of operations where network information for setting the home link is acquired when the device is activated, parameters of the home link and the home agent are set, and the home agent is activated to start accommodating the mobile terminal, is not prescribed. Thus, it is required for a user to conduct the parameter setting manually. Especially, in IPv6 systems, since an IP address is a long address of 128 bits, the manual setting of the above parameter takes considerable effort.
Additionally, in the JP-A-2001-24710, the representative server which corresponds to the home gateway device receives the allocation of the address block from the connecting network. In order to make the server operate as the home agent, it is necessary that information based on the mobile IP is manually set to a communication interface connected to the home link. Particularly in the case of replacing the home gateway device, if there are existing mobile terminals, it is required to maintain as much as possible the settings of the home link included in these terminals and not to compel change of mobile terminal settings.
Furthermore, it is preferable that the home link is arranged in the home network, and it is necessary in an automatic setting thereof to appropriately select the communication interface which should serve as the home link.